This invention relates to method and apparatus for applying liquid lubricant to the surface of flexible cores or the like, particularly as a preliminary step in the production of flexible tubular articles.
In the manufacture of long lengths of small diameter hose, a pre-cured flexible rubber rod, known as a mandrel, is used as a core on which the hose is constructed and cured. In the case of rubber hose, curing is effected by vulcanization. Most plastic hose, on the other hand, becomes cured or heat set immediately upon extrusion at room temperature. In either case, upon curing the hose, the mandrel, which may be as long as 1200 feet or more, must be removed from the hose and this is normally done using high pressure water. In addition, to prevent sticking of the mandrel to the interior tube of the hose a release agent (lubricant) is applied to the surface of the mandrel. A graphite mixture has traditionally been used as a release agent, however residual graphite left in the tube of the hose must be removed by a washing step to meet hose cleanliness requirements.
Silicone oil and other clean fluids have been used as lubricant substitutes for graphite. The silicone is customarily applied by passing the mandrel through a tank containing a silicone thinned with a solvent, and then guiding the mandrel through a wiper. However, this system is beset with critical drawbacks. It is extremely difficult to apply a uniformly thin coating of the silicone on the mandrel surface. Oftentimes too thin a mixture is applied to all or a portion of the circumference of the mandrel, and this causes sticking leading to difficulty in removal of the mandrel from the cured hose. When the solvent mixture applied is too thick, localized pools of lubricant mixture are created between the mandrel and hose tube, leading to the creation of undesirable pinholes in the hose tube. Moreover, with the silicone/solvent system, solvent vapor emissions introduce vapor control costs, fire hazards and quality control costs not to mention the added cost of the solvent.
It is a primary object of the subject invention to provide a system for lubricating flexible mandrel without the aforementioned problems, wherein a carefully controlled thin coating of lubricant, substantially undiluted by solvent, is applied generally uniformly to the surface of the mandrel, and without requiring significant further processing.